Certain phthalazine 4-yl acetic acid derivatives are disclosed in U.S. Pat. No. 4,251,528 to Brittain et al and such generic and specific disclosure includes 3 [(4-bromo 2 fluorophenyl)-methyl]-3,4 dihydro 4 oxo-1-phthalazineacetic acid. The process disclosed for the preparation of such compound generally involves the protection of the carboxylic acid group with the preparation of an ester thereof. Thus, the synthesis of the product involved the preparation of a lower alkyl ester of 3,4-dihydro-4-oxo-1 phthalazineacetic acid, the alkylation of the 3-position ring nitrogen to form the esterified product and deesterification to form the product. Three steps were thus involved and yields are stated to be about 36% overall for the alkylation and deesterification reactions. In the same Brittain et al reference one example is given of a direct alkylation of the unesterified carboxylic acid, however the yields are only about 15% or less. Additional attempts to prepare the above product using the unesterified carboxylic acid and the conditions described in Brittain et al have resulted in the preparation of negligible amounts of the product. The instant improved process involves direct alkylation of the unprotected carboxylic acid. It thus avoids the time and expense of esterification and deesterification and most surprisingly, directly produces the desired compound in yields approaching 90%.